The graphene is a wonderful material and it can be the realization of two-dimensional electron gas. Indeed when flat geometry is realized it has an electrical conductivity similar to that of copper and unbeaten thermal conductivity. Graphene could pave the way to several technological applications, such as conductive inks, ultrahigh-frequency transistors and photovoltaic devices. In practice, it deviates from planar geometry because of ripples probably induced also by undesired impurities (*). Few days ago, scientists from the University at Buffalo, the National Institute of Standards and Technology (NIST), the Molecular Foundry at Lawrence Berkeley National Laboratory (Berkeley Lab), and SEMATECH, published on Nature C0mmunications the results of a research that with X-ray and synchrotron radiation techniqes allowed the imaging of the local electronic corrugations alongside inhomogeneously doped regions of single graphene sheet. Here the press release from UB.
Beside scanning transmission X-ray microscopy (STXM) imaging, and in situ near edge X-ray absorption fine structure (NEXAFS) spectroscopy experiments, the combined use of density functional theory calculations helped to improve the understanding of deviations from the ideal behavior of graphene spectra.
(*) Update: in general ripples are formed on graphene due to random corrugations that compensates random thermal fluctuations and because of the substrate. However in this experiment samples are doped.
Update 2: A recent viewpoint by Michael Baum confirmed the vision that contaminants and ripples (or wrinkles) are connected. The electrical properties of graphene are so degraded by contaminants, that are believed to be just physisorbed rather than chemisorbed (like in doping). Once understood this we have also physical processes able to free samples by contaminants and restore the conductivity of pure graphene, e.g. by heating.
In conclusion the ideal behavior of graphene is corrupted by contaminants, and new ways to eliminate them are required if we want to exploit the wonderful properties of this innovative material.